1. Field of the Disclosure
Aspects of the present disclosure relate to ultrasonic transducers, and, more particularly, to methods of forming a connection with a piezoelectric micromachined ultrasonic transducer defining an air-backed cavity, and associated apparatuses.
2. Description of Related Art
Some micromachined ultrasonic transducers (MUTs) may be configured, for example, as a piezoelectric micromachined ultrasonic transducer (pMUT) as disclosed in U.S. Pat. No. 7,449,821 assigned to Research Triangle Institute, also the assignee of the present disclosure, which is also incorporated herein in its entirety by reference.
The formation of pMUT device, such as the pMUT device defining an air-backed cavity as disclosed in U.S. Pat. No. 7,449,821, may involve the formation of an electrically-conductive connection between the first electrode (i.e., the bottom electrode) of the transducer device, wherein the first electrode is disposed within the air-backed cavity of the pMUT device, and the conformal metal layer(s) applied to the air-backed cavity for providing subsequent connectivity, for example, to an integrated circuit (“IC”) or a flex cable.
In some instances, one or more pMUTs, for example, arranged in a transducer array, may be incorporated into the end of an elongate catheter or endoscope. In those instances, for a forward-looking arrangement, the transducer array of pMUT devices must be arranged such that the plane of the piezoelectric element of each pMUT device is disposed perpendicularly to the axis of the catheter/endoscope. Where the transducer array is a one-dimensional (1D) array, external signal connections to the pMUT devices may be accomplished by way of a flex cable spanning the series of pMUT devices in the transducer array so as to be in electrical engagement with (i.e., bonded to) each pMUT device via the conformal metal layer thereof. For instance, in one exemplary 1D transducer array 100 (e.g., 1×64 elements), pMUT devices forming the array elements 120 may be attached directly to a flex cable 140, with the flex cable 140 including one electrically-conductive signal lead per pMUT device, plus a ground lead. For a forward-looking transducer array, the flex cable 140 is bent about the opposing ends of the transducer array such that the flex cable 140 can be routed through the lumen of the catheter/endoscope which, in one instance, may comprise an ultrasound probe. However, for a forward-looking transducer array in a relatively small catheter/endoscope, such an arrangement may be difficult to implement due to the severe bend requirement for the flex cable (i.e., about 90 degrees) in order for the transducer array to be disposed within the lumen of the relatively small catheter/endoscope.
Moreover, for a forward-looking two-dimensional (2D) transducer array, signal interconnection with the individual pMUT devices may also be difficult. That is, in an exemplary 2D transducer array (e.g. 14×14 to 40×40 elements), there may be many more required signal interconnections with the pMUT devices, as compared to a 1D transducer array. As such, more wires and/or multilayer flex cable assemblies may be required to interconnect with all of the pMUT devices in the transducer array. However, as the number of wires and/or flex cable assemblies increases, the more difficult it becomes to bend the larger amount of signal interconnections about the ends of the transducer device to achieve the 90 degree bend required to integrate the transducer array into a catheter/endoscope. Accordingly, such limitations may undesirably limit the minimum size (i.e., diameter) of the catheter/endoscope that can readily be achieved.
Thus, there exists a need in the ultrasonic transducer art, particularly with respect to a piezoelectric micromachined ultrasound transducer (“pMUT”) having an air-backed cavity, for improved methods of forming an electrically-conductive connection between the pMUT device and, for example, an integrated circuit (“IC”) or a flex cable. More particularly, it would be desirable for such an electrically-conductive connection with the pMUT device to be configured to avoid bending of the flex cable/wiring about the pMUT device upon integration thereof in the tip of a probe/catheter/endoscope used, for example, in cardiovascular devices and intravascular ultrasound devices. Such solutions should desirably be effective for 2D transducer arrays, particularly 2D pMUT transducer arrays, but should also be applicable to 1D transducer arrays, and should desirably allow greater scalability in the size of the probe/catheter/endoscope having such transducer arrays integrated therein.